The relationships between structure and function in electron transport proteins and in metalloenzymes will be examined. Electron spin echo (ESE) spectroscopy will be employed to measure magnetic interactions among redox components in the cytochrome bc1 complex (Complex III) from yeast, from both wild-type and mutant (photosynthetically deficient) photosynthetic bacteria, and from bovine heart. The structure and environment of the Rieske Fe/S cluster, and its interaction with the apparent ubiquinol oxidation site (QZ) will be examined, using inhibitors specific for this site. Interactions of cytochromes b and c1 with the Rieske cluster will be measured as well. The structures of the three Fe/S clusters in bovine heart succinate dehydrogenase (SDH) will also be investigated, as a model for intact Complex II. Spin relaxation enhancement of the S-1 (2Fe2S) (+1, +2) cluster by the faster-relaxing S-2 and S-3 (S = 2 state) clusters will be measured, using the ESE spectrometer. Calculations will be made of the distances between and angle among the clusters, using data from oriented mutilayers of SDH. Improved theoretical tools will be developed for the prediction of the three-dimensional structures of proteins, particularly membrane-bound proteins, from their amino acid sequences. New methods of analyzing sequences homology among proteins will also be developed. The chemical and electronic environment of Mn(II) in three enzymes and in crystalline model complexes will be examined by electron spin echo envelope modulation (ESEEM) and by electronnuclear double resonance (ENDOR). Hypotheses regarding the function of the metal in the catalytic mechanisms of the enzymes will be testes. Improvements will be made to our low-power ESE spectrometer. An ENDOR facility to be added to our standard EPR spectrometer will be employed to measure strong ligand superhyperfine couplings.